In India one of the major mode of transport is Bus. Now in India most of the state tourism and transport departments are running inter-state and intra-state buses(comfortable luxury a/c coaches like volvo) that network among the tourist destinations and many Indian cities. 
There are many Bus services in India which includes both governmental and non government services. So many prominent online bus ticket service providers available in Indian market.

Useful links to know more about the transportation in India and
Online bus ticket booking portals :
1. Red bus
2. Ticket vala
3. Book Cheapest
4. India bus transportation
5. Abhi Bus
6. Kallada Travels
7. Andhra Pradesh RTC
8. Karnataka RTC
9. Kerala RTC
10. Customer Needz
11. ABT Travels
12. Dhanunjaya Travels
13. Sree Kaleswari Travels
14. Kesineni Travels
15. USL National Express
16. Ticket Goose
17. Go 4 Ticket
18. KPN Travels
19. Net Ticket 4u
20. Paulo Travels
21. Vijayanand Travels
22. Raj Travels